When HostMonitor starts as a service, it uses the system account (as all interactive services). But this account may not have all the necessary permissions, so some tests will not work correctly (UNC test, "disk free space" test for shared drives, "CPU Usage" test for remote machines, etc). If you need these tests, you will need to assign a special user account on the Service page in the Options dialog. In this case HostMonitor will impersonate the security context of the user. Do not change the account using the system utility "Services". If you do so, HostMonitor may be unable to interact with the desktop.
Please, read the manual:
http://www.ks-soft.net/hostmon.eng/mframe.htm#other.htm#Servicehttp://www.ks-soft.net/hostmon.eng/mframe.htm#options.htm#Service